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#21 | Link |
I'm Siri
Join Date: Oct 2012
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Posts: 2,633
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shit won't happen to the color if you applied a casual twisted color system to some vid, it shares the same CIE result like the one with a "scientific" color system anyways, doesn't really matter if the vid is 4:4:4, scientific or not, it always leads to the same CIE value, and that's why matrix like "YCgCo" exists.
but if the vid got a subsampled chroma, that would be a whole new story, the wrong matrix would send some luminance to chroma planes, and chroma planes will be subsampled and we all know what will happen next... |
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#23 | Link |
I'm Siri
Join Date: Oct 2012
Location: void
Posts: 2,633
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And I'm not really sure what was the question
Like I said, shit won't happen color wise, the down side is subsample related, if subsample didn't exist, YCgCo would be way better than 601 or 709, it gives zero rounding error converting between YUV and RGB |
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#24 | Link | ||
Super Moderator
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Location: Netherlands
Posts: 6,370
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The general consensus nowadays is that Rec601 should be assumed for dvd's, regardless when the colorimetry is present in the header. I'm not saying that's wrong, but we can't be 100 percent sure unless some actually got that from the dvd specs itself. Btw, where is the quote "encoded using a different set of coefficients as used by AviSynth's color conversion routines" coming from? Perhaps i wrote that one day, but it is not in the current (or 2007) documentation. Last edited by Wilbert; 15th August 2015 at 22:52. |
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#25 | Link | |||
契約者
Join Date: Jun 2008
Posts: 1,576
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Edit: found some old ones. dgmpgdec150+ assume rec601. Quote:
Edit: By the way, first english-language link in google leads here, where it says something different: Quote:
Last edited by Keiyakusha; 16th August 2015 at 04:36. |
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#26 | Link | ||
ekTOMBE STUDIOS
Join Date: Dec 2005
Location: Cuba
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So, it works or not??? |
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#27 | Link |
Registered User
Join Date: Oct 2011
Posts: 204
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I see so many people here who ask themselves what can be done for people who use buggy software (video decoders that don't pass the colorimetry information to the video renderer, video renderers that ignore colorimetry information that they get from the decoder), so I feel I should raise the question of whom this truly benefits:
* If anyone is going to mention ffdshow and avisynth processing, I'm just going to tell them to manually insert colormatrix into the avisynth script themselves, if ffdshow can't handle colorimetry. You'll notice that I have little to no sympathy for people who use broken software. I think that is all right, though, because it's already 2015, and stuff like LAV Filters, which respects colorimetry information, has been around for a long time already. Additionally, I remember that, also quite a while back, MPC-HC fixed EVR (perhaps only EVR-CP, I don't remember that well) to respect colorimetry information also, so the point that there are too few common video renderers that respect colorimetry information, if present, is also invalid. You'll also notice that I only mentioned software. If the goal is playback on hardware players, then my reasoning becomes invalid, because then the act of "simply switching playback environments" becomes that much harder. And although I'm still in favor of using something that actually does it right for playback, even in those cases, I can acknowledge that this is unreasonable. |
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#28 | Link | |
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Join Date: Mar 2011
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I'm still runing XP on the PC I use as a media player. I have no particular need to change OS. It works fine. I'm fairly certain the colorimetry info is ignored when using the MPC-HC/EVR combination just as it is with most other renderers. I could use MadVR, but I prefer not to.
I care about colorimetry. It's why, - I always use rec.601 for SD and rec.709 for HD. - If I need to correct the colorimetry on playback, I can do it manually with a pixel shader. Or several other ways. I'm still not clear as to how converting the colours "harms those who are already doing it right" (those using software that obeys the colorimetry, I assume), and in the real world encoded video is rarely only played back using a single device, software or hardware, and my switching to different playback software has no effect on the colorimetry that'll be used by the media player built into the TV in the family room, or the Bluray player connected to the TV in the living room etc. Using a colorimetry which is "most likely" to be displayed correctly seems logical to me. Quote:
Maybe there's no longer encoders like that, but the HCenc encoder is mentioned here: Color coefficients and Colormatrix usage summary (Q and A) Last edited by hello_hello; 17th August 2015 at 07:37. |
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#29 | Link |
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Join Date: Mar 2011
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I have a Bluray video. I re-encode it. I use no other filtering aside from colormatrix to change the colorimetry to rec.601.
(Of course normally I wouldn't do so unless I was downscaling to SD). On playback I use a player that obeys the colorimetry info written to the video stream. I use the same TV/monitor each time. The original Bluray video would look like this: Color primaries : BT.709 Transfer characteristics : BT.709 Matrix coefficients : BT.709 After I convert the colours, I'd tell x264 to write this: Color primaries : BT.709 Transfer characteristics : BT.709 Matrix coefficients : BT.601 The question was, how/why would they display differently? I'm not sure how your references to subsampling apply. Last edited by hello_hello; 17th August 2015 at 07:48. |
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#30 | Link | |
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Join Date: Mar 2011
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I still don't understand why that was best practice for years, but because x264 has the ability to write the colorimetry info, it's now a sin to follow the same rule. |
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#31 | Link | |
I'm Siri
Join Date: Oct 2012
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#32 | Link |
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Join Date: Mar 2011
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Well that makes me feel a bit better. If there was a reason why converting the colours would have a detrimental effect, I'd reconsider whether doing so was a good idea. Is there a circumstance when converting the colours that way while re-encoding video would be detrimental?
Of course much of the time the colour primaries, transfer characteristics and matrix coefficients aren't known. I just checked a Bluray rip on my hard drive and MediaInfo doesn't show info for any of them. So I guess all I can do is assume the source matrix coefficients are rec.709 and write that to the video stream when encoding, or write rec.601 if converting the colours. My understand is it's best not to specify anything for colour primaries or transfer characteristics unless you actually know what they should be, so unless I do, I don't. I assume that's the right thing to do? |
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#33 | Link | |
I'm Siri
Join Date: Oct 2012
Location: void
Posts: 2,633
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Q2: I guess so. EDIT: the precise and more correct way to convert from HD to SD, SD to HD likewise 0. expand to PC range 1. resample to 444 2. convert to gamma compressed RGB with matrix "709" 3. convert to linear RGB with "709" transfer 4. convert to CIE XYZ with "709" primaries 5. convert to CIE Lab 6. scale to SD 7. convert back to CIE XYZ 8. convert to linear RGB with "601 NTSC" or "601 PAL" primaries 9. apply "709" transfer 10. apply "601" matrix 11. resample to 422/420 or keep it as 444 12. shrink to TV Range Last edited by feisty2; 17th August 2015 at 12:13. |
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#34 | Link |
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So when I asked earlier if the example source and encode will display the same way, the answer was yes, because the colours will display the same way, but now it's no because the luminance might be a little different?
To be honest, about the only time I convert the colours is when downscaling, or if for some reason I think the source was encoded with the wrong colorimetry, and if I'm re-encoding/downscaling I'm probably going to be applying other filtering such as noise removal and/or sharpening anyway. I might try the 12 step colour conversion method one day, but if I'm taking a high definition video and downscaling it to standard definition it'd have to offer a noticeable quality improvement. Considering the "damage" already being inflicted on the picture through downscaling and other filtering, I'm not sure it'd make enough difference to matter. |
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#35 | Link | |
47.952fps@71.928Hz
Join Date: Mar 2011
Posts: 940
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This almost looks like the dither_resize16 process. Dither_convert_yuv_to_rgb(...) Dither_y_gamma_to_linear Dither_resize16 Dither_y_linear_to_gamma Dither_convert_rgb_to_yuv(...) Except, I dont apply 444 and PC range first (and TV range last, then 420/422). (and also don't do that CIE XYZ & CIE LAB thingy) I've always been curious about that, though. For DVD processing.
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#36 | Link | |
I'm Siri
Join Date: Oct 2012
Location: void
Posts: 2,633
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Quote:
Dither_convert_yuv_to_rgb(...) = 0. 1. 2. Dither_y_gamma_to_linear = 3. Dither_resize16 Dither_y_linear_to_gamma = 9. Dither_convert_rgb_to_yuv(...) = 10. 11. 12. |
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#38 | Link | |
I'm Siri
Join Date: Oct 2012
Location: void
Posts: 2,633
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Quote:
CIE Lab is required to prevent linear light artifacts (dark halo, see http://www.imagemagick.org/Usage/resize/#resize_lab) |
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#39 | Link |
47.952fps@71.928Hz
Join Date: Mar 2011
Posts: 940
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Interesting reads.
Although, tyring to implement to YV12 movies (AVC/VC-1/MPEG2) with avisynth, I can't see myself converting a whole movie to PNGs for a process. Still going through some limited google searches to this forum for CIE LAB. There's a lot to catch up with and read. Got myself a good mini-ebook to compile here.
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blu-ray, color, colormatrix, correction, h264 |
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